Understanding Security Scanners

How DAST and SAST Work Under the Hood

Security scanners are automated tools that detect vulnerabilities in applications. They come in two main categories: Dynamic Application Security Testing (DAST) and Static Application Security Testing (SAST).

Both approaches are essential for comprehensive security coverage, but they work in fundamentally different ways and catch different types of vulnerabilities.

🎯Why Security Scanners Matter

⚡ Speed and Scale

Automated scanners can test thousands of attack vectors in minutes, something impossible with manual testing alone.

🔄 Continuous Security

Integrate into CI/CD pipelines to catch vulnerabilities before they reach production.

📊 Comprehensive Coverage

DAST finds runtime vulnerabilities, SAST catches code-level issues - together they provide complete coverage.

💰 Cost Effective

Finding vulnerabilities early in development is 100x cheaper than fixing them in production.

🌐DAST: Dynamic Application Security Testing

DAST tools test running applications from the outside, simulating how an attacker would probe your web application. They don't need access to source code - they work like a hacker, sending malicious payloads and analyzing responses.

How DAST Works: Technical Workflow

🕷️

1. Crawling / Spidering

The scanner discovers all endpoints, pages, and functionality in your application.

Starts from a seed URL (usually the homepage)
Follows all links, forms, and JavaScript-generated content
Builds a complete sitemap of URLs, parameters, and entry points
Discovers hidden directories and files (robots.txt, sitemap.xml)
Identifies API endpoints and AJAX calls
Maps out the application's attack surface

🔐

2. Authentication & Session Management

Handles login and maintains authenticated sessions to test protected areas.

Records authentication flows (login, OAuth, SSO)
Maintains session cookies and tokens
Handles multi-step authentication (2FA, CAPTCHA bypass in test environments)
Tests session timeout and logout functionality
Checks for session fixation and hijacking vulnerabilities
Verifies proper session invalidation

⚔️

3. Active Vulnerability Scanning

Sends malicious payloads to every input point discovered during crawling.

SQL Injection: Tests database query manipulation with special characters, UNION attacks, boolean/time-based blind injection
Cross-Site Scripting (XSS): Injects JavaScript payloads to test reflection, storage, and DOM manipulation
Command Injection: Tests OS command execution through input fields
Path Traversal: Attempts to access files outside web root using ../ sequences
XXE (XML External Entity): Tests XML parsers for external entity injection
SSRF: Attempts to make the server request internal/external resources
Authentication Bypass: Tests for broken authentication and authorization
CSRF: Checks for missing anti-CSRF tokens

🔍

4. Response Analysis

Analyzes server responses to determine if vulnerabilities exist.

Checks HTTP status codes and error messages
Looks for database error messages indicating SQL injection
Detects reflected payloads in HTML responses (XSS)
Measures response times for blind injection attacks
Analyzes HTTP headers for security misconfigurations
Validates SSL/TLS certificates and cipher suites
Checks for sensitive data exposure in responses

📊

5. Reporting & Verification

Generates detailed reports and reduces false positives.

Categorizes findings by severity (Critical, High, Medium, Low)
Provides proof-of-concept payloads for each vulnerability
Includes exact request/response pairs
Maps findings to OWASP Top 10 and CWE classifications
Offers remediation guidance and code examples
Attempts to verify and reduce false positives

Key Advantage: DAST finds vulnerabilities in the running application, including configuration issues, server-side problems, and complex multi-step attacks that only appear at runtime.

📝SAST: Static Application Security Testing

SAST tools analyze source code, bytecode, or binary without executing the application. They work like a code reviewer, looking for insecure patterns, dangerous functions, and vulnerable code paths.

How SAST Works: Technical Workflow

📄

1. Source Code Parsing

Reads and parses source code into analyzable structures.

Supports multiple languages (Java, C#, Python, JavaScript, PHP, Ruby, Go, etc.)
Parses code into tokens and syntax trees
Handles compiled code (bytecode, binaries) when source isn't available
Resolves imports, includes, and dependencies
Builds a complete model of the application structure

🌳

2. Abstract Syntax Tree (AST) Generation

Converts code into a tree structure representing its logical structure.

Represents code as a hierarchical tree of nodes
Each node represents a construct (function, loop, condition, variable)
Enables deep semantic analysis beyond simple pattern matching
Allows tracking of data flow across complex code paths
Preserves relationships between functions, classes, and modules

🔄

3. Data Flow Analysis

Tracks how data moves through the application from sources to sinks.

Sources: User input (HTTP parameters, cookies, files, databases)
Sinks: Dangerous functions (SQL queries, system commands, eval())
Traces data from entry point to dangerous operation
Identifies if user input reaches a sink without sanitization
Handles complex flows through multiple functions and files
Detects second-order vulnerabilities (stored XSS, delayed SQL injection)

🔀

4. Control Flow Analysis

Analyzes the order in which code executes and possible execution paths.

Maps all possible execution paths through the code
Identifies dead code and unreachable paths
Detects authentication bypasses and logic flaws
Checks for missing security checks before operations
Analyzes conditional branches and loops
Finds race conditions and concurrency issues

☣️

5. Taint Analysis

Tracks "tainted" (untrusted) data to ensure it's sanitized before use.

Marks all user input as "tainted"
Tracks tainted data through variables, functions, and objects
Identifies sanitization functions that remove taint
Flags when tainted data reaches a dangerous operation
Detects insufficient or incorrect sanitization
Handles complex propagation through encodings and transformations

🎯

6. Security Pattern Matching

Identifies known insecure coding patterns and anti-patterns.

Hardcoded credentials and API keys
Use of weak cryptographic algorithms (MD5, SHA1, DES)
Insecure random number generation
Dangerous functions (eval, exec, system, unserialize)
Missing input validation or output encoding
Insecure deserialization
Missing security headers and configurations

📋

7. Reporting & Prioritization

Generates actionable reports with precise code locations.

Shows exact file, line number, and code snippet
Provides data flow path from source to sink
Categorizes by vulnerability type and severity
Includes remediation code examples
Maps to OWASP Top 10, CWE, and compliance standards
Integrates with IDEs for real-time feedback

Key Advantage: SAST catches vulnerabilities early in development before code is deployed. It finds issues in code paths that might be difficult to reach with DAST, and provides exact locations for fixes.

⚖️DAST vs SAST: Key Differences

Aspect	DAST	SAST
Testing Approach	Black-box (outside-in)	White-box (inside-out)
Requires Running App	✅ Yes	❌ No
Needs Source Code	❌ No	✅ Yes
When to Run	QA, Staging, Production	Development, Pre-commit, CI/CD
Speed	Slower (hours)	Faster (minutes)
False Positives	Lower	Higher
Finds Runtime Issues	✅ Yes (config, server)	❌ No
Shows Exact Code Line	❌ No	✅ Yes
Best For	XSS, SQLi, auth bypass, config	Hardcoded secrets, insecure crypto, injection flaws

✅Best Practices: Using Both Together

1️⃣

Start with SAST Early

Run SAST in the IDE and on every commit. Catch issues before they're committed.

2️⃣

Use DAST in QA/Staging

Run DAST against deployed environments to catch runtime and configuration issues.

3️⃣

Automate in CI/CD

Integrate both scanners into your pipeline. SAST on build, DAST after deployment.

4️⃣

Don't Rely on One

SAST and DAST catch different vulnerabilities. Use both for comprehensive coverage.

5️⃣

Verify and Prioritize

Manually verify critical findings. Focus on exploitable vulnerabilities first.

6️⃣

Tune Your Scanners

Configure authentication, reduce false positives, and customize rules for your stack.